Weed research may yield flowers that last longer University of Pennsylvania studying arabidopsis in $12 million project

April 17, 1997|By KNIGHT-RIDDER NEWS SERVICE

PHILADELPHIA - University of Pennsylvania scientists are growing a garden full of weeds, tending them with the kind of loving care usually reserved for prize begonias.

The weeds are part of a $12 million research project designed to identify every gene in the cells of the plant arabidopsis, much the way the $3 billion human genome project will map the genes in human cells.

Researchers say this plant genome project, headed by Penn biologist Joseph Ecker, will hand humankind new power to alter the plant kingdom at will, creating strains of wheat and other grains that can grow in the desert or resist drought; tomatoes whose ripening can be orchestrated so they hold up during shipping but turn juicy and ripe on supermarket shelves; roses that don't wilt for weeks; bizarre new plants that produce plastic or other chemicals; and even plants that soak up toxic waste.

Shares 20,000 genes

But why study a weed?

Because of the close genetic ties within the plant kingdom, weeds aren't so different from more useful plants.

Arabidopsis shares most of its 20,000 genes with corn, wheat, tomatoes and other important food crops.

Moreover, the qualities that make arabidopsis so weedy and bothersome are exactly those that make it good for science. It grows and reproduces fast, turning out new generations in just six weeks.

Similar qualities have made scientists fond of rats, mice and fruit flies.

Weeds are also well suited to the crowded urban landscape of West Philadelphia, says Ecker. He points to a few stalks of corn growing in one of a series of glass-enclosed growing rooms in his lab. "We don't have space for very much of this."

The Penn group is collaborating with weed labs at Stanford University and the University of California, Berkeley. By 2004, they expect to be finished locating every gene in the plant's five chromosomes and learning what most of those genes do.

Though some people began studying arabidopsis in the 1960s, says Ecker, "no one recognized its importance because it was just a weed."

Ecker and his colleagues purposely make mutant plants - plants with different defective genes. Some grow abnormally large, or have flowers with too many petals, or make no green pigment, says Ecker. The plants with mutations help tell them what the damaged genes do in normal plants.

But the hardest part of the project is what the scientists call sequencing - a way of "reading" the genetic code written into the material that makes up the genes, the DNA.

Arabidopsis carries 100 million of these code characters, also called base pairs. Human chromosomes have 3 billion.

So far, Ecker's lab has sequenced 200,000 of these code elements - less than 1 percent of the goal.

The main purpose of the sequencing will be to help scientists not only match genes with specific traits, but also learn how the genes do it.

The field of genetics started with plants: The peas that Austrian monk Gregor Mendel bred and crossbred in the mid-19th century provided the basis for the first laws of genetics. But now plants are underrepresented in genetics, says Eliot Meyerowitz, a plant biologist at the California Institute of Technology.

Scientists are spending 100 times the cost of the plant genome project on its human counterpart. "The national funding priorities are skewed toward direct medical research. ... We use plants for everything, so we should pay more attention to them in our research budget," Meyerowitz said.

Studies paying off

Already, studies of arabidopsis are paying off in more useful and tastier plants.

Last year, for example, Ecker and Meyerowitz identified a mutant strain of arabidopsis whose flowers don't wilt normally. They connected that trait with a gene that blocks the way plants respond to ethylene - a common pollutant that, in plants, acts as a hormone controlling not only wilting, but also the ripening of fruit.

Ethylene is used by tomato growers to make them "ripen" because they are picked while still green and hard enough to ship. The trouble, Ecker says, is that the tomatoes taste terrible because the artificial ripening process doesn't give them time to develop much flavor.

Ecker and Meyerowitz used their ethylene-sensitivity gene in weeds to find the analogous gene in a tomato.

They realized they could partly suppress this gene, in that way adjusting the ripening of the tomatoes so that they would remain green while being shipped but arrive on supermarket shelves ready to eat.

The researchers sold their idea to Monsanto, though the company has not yet come out with the dream tomato.

Petunia plants also share such a gene, and using various techniques to block its function, scientists can make flowers that last longer before wilting.

Soaking up pollution

Penn plant researcher Philip Rea is trying to genetically engineer an arabidopsis mutant that would soak up heavy metals, a dangerous form of pollution.

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